CN114222387A - Method for improving microwave heating temperature uniformity - Google Patents
Method for improving microwave heating temperature uniformity Download PDFInfo
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- CN114222387A CN114222387A CN202111410642.5A CN202111410642A CN114222387A CN 114222387 A CN114222387 A CN 114222387A CN 202111410642 A CN202111410642 A CN 202111410642A CN 114222387 A CN114222387 A CN 114222387A
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
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Abstract
A method for improving the uniformity of microwave heating temperature is characterized in that an auxiliary material containing a temperature-sensitive electromagnetic material is added inside, outside or both inside and outside a material, so that the temperature rise capability of the whole material or a certain local area in a required temperature interval is reduced along with the temperature rise, and the temperatures of a hot area and a cold area in the whole material or the certain local area in the temperature interval are closer. The invention can greatly improve the temperature uniformity of microwave heating, does not need complex temperature monitoring means and has wide application range.
Description
Technical Field
The invention relates to a composite material microwave heating technology, in particular to a method for improving the temperature uniformity of composite material microwave heating, and specifically relates to a method for improving the temperature uniformity of a heated material in a microwave heating process.
Background
The microwave is an electromagnetic wave having a frequency of 300M to 300 GHz. Microwave heating is an energy-saving and efficient heating mode, has a series of advantages of high heating speed, selective heating, easiness in control and the like, and is widely applied to various fields of food processing, material treatment, chemical synthesis and the like. However, the non-uniform distribution of the electromagnetic field in the microwave cavity causes non-uniform temperatures in the relatively hot regions (hot zones) and relatively cold regions (hot zones) on the material. This problem seriously affects the heating quality of the material and hinders the application of microwave heating technology.
The existing methods for improving the uniformity of microwave heating temperature mainly comprise three methods: (1) the electromagnetic field distribution in the cavity is optimized before heating, and the electromagnetic field distribution in the cavity is more uniform by optimizing the shape and size of the microwave cavity or the position of the microwave source. But the nature of the resonance of the electromagnetic wave in the cavity determines that this method cannot in principle achieve a uniform distribution of the electromagnetic field. (2) On the basis, random relative motion (such as using a material rotating tray or a mode stirrer or the like) is generated between the electromagnetic field and the heated material in the heating process, so that the uniformity of microwave heating can be further improved on the whole, but the situation that a cold area is cooler and a hot area is hotter in the local part of the material cannot be avoided. (3) Therefore, based on the real-time monitoring result of the material temperature distribution in the heating process, the directional compensation of the uneven temperature field is a new idea in recent years, but the further development of the temperature field monitoring technology (especially the surface temperature measurement technology) is also needed.
Compared with the prior art, the invention provides that the auxiliary material containing the temperature-sensitive electromagnetic material is added in, outside or inside and outside the material simultaneously, so that the heating capacity of the whole material or a certain local area in a required temperature interval is reduced along with the temperature rise, and the heating capacity of a hot area in the whole material or a certain local area in the temperature interval is lower than that of a cold area, so that the temperatures of the hot area and the cold area are enabled to be closer (the relevant principle is shown in figure 1). The invention does not need to monitor the temperature distribution of the material in real time, but can achieve the effect of directional compensation on the temperature field, and has easy implementation and wide application prospect.
Disclosure of Invention
The invention aims to provide a novel method for improving the uniformity of microwave heating temperature aiming at the problem of nonuniform temperature distribution of heated materials in microwave heating, and breaks through the problem of nonuniform microwave heating in principle.
The technical scheme of the invention is as follows:
a method for improving the uniformity of microwave heating temperature is characterized in that: the auxiliary material containing the temperature-sensitive electromagnetic material is added in, outside or both the inside and the outside of the material, so that the heating capacity of the whole material or a certain local area in a required temperature interval is reduced along with the temperature rise, and the heating capacity of a hot area in the whole material or a certain local area in the temperature interval is lower than that of a cold area, so that the temperatures of the hot area and the cold area are enabled to be closer.
The auxiliary material containing the temperature-sensitive electromagnetic material is added into the material, namely powder containing the temperature-sensitive electromagnetic material is mixed in the material, so that the material can obtain the wave absorbing performance which is reduced along with the temperature rise in a required temperature range.
The powder of the temperature-sensitive electromagnetic material is one or a mixture of more of particles such as strontium titanate, barium titanate or barium strontium titanate.
The method for mixing the temperature-sensitive electromagnetic material in the material is determined according to the aspects of the shape, the size and the like of the material, such as melt blending, mechanical blending and the like.
The auxiliary material containing the temperature-sensitive electromagnetic material is added outside the material, namely a temperature-sensitive film with a two-layer or multi-layer structure is covered outside the material; the temperature-sensitive film is composed of one or more dielectric layers and one or more sub-wavelength conductive patterns, and at least one dielectric layer or conductive pattern is made of or contains a temperature-sensitive electromagnetic material, so that the wave absorbing performance of the whole temperature-sensitive film and material is reduced along with the temperature rise in a required temperature interval.
The conductive pattern has a negligible dimension in the thickness direction (less than 500 microns), has a specific geometry in the plane, and its shape and dimensions are easily determined by electromagnetic simulation in the case of material selection (i.e. material parameter determination).
The auxiliary material containing the temperature-sensitive electromagnetic material is added outside the material, namely, the wave-absorbing material is covered outside the material; the wave-absorbing material is made of or comprises a temperature-sensitive electromagnetic material, and has wave-absorbing performance which is reduced along with the temperature rise in a required temperature range, so that heat is transferred to a heated material more uniformly after microwave is absorbed.
When the auxiliary material containing the temperature-sensitive electromagnetic material is added outside the material, special attention needs to be paid to ensure that the auxiliary material is in close contact with the heated material, and the method can be realized by methods such as coating, attaching, plating, vacuum adsorption and the like.
The temperature-sensitive electromagnetic material refers to a material with electromagnetic parameters changing along with temperature; alloys of metals such as copper, aluminum, silver, chromium, etc., phase-change metal oxides such as vanadium dioxide, etc., ferroelectric materials such as strontium titanate, barium titanate, etc., liquid crystal materials, and materials containing the above components.
The electromagnetic parameters refer to resistivity, dielectric constant, magnetic permeability or a combination of the above parameters.
The invention has the beneficial effects that:
the invention does not need to monitor the temperature distribution of the material in real time, but can achieve the effect of directional compensation on the temperature field, and has easy implementation and wide application prospect.
Drawings
FIG. 1 is a schematic diagram of the process of the present invention.
FIG. 2 is a schematic view of a two-layer structure temperature-sensitive membrane of the present invention.
FIG. 3 is a schematic diagram showing the change of real part of dielectric constant with temperature at a frequency of 2.45GHz in a temperature-sensitive film with a double-layer structure according to the present invention.
FIG. 4 is a schematic diagram showing the change of the 2.45GHz microwave absorption rate with temperature of the whole temperature-sensitive film with the double-layer structure and the carbon fiber reinforced epoxy resin-based composite material.
Detailed Description
The method scheme of the invention will be described clearly and completely with reference to the accompanying drawings of the embodiment of the invention, and obviously, the described embodiment is only a part of the embodiment of the invention. Rather than all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the scope of protection of the present invention.
As shown in fig. 1.
The method for improving microwave heating temperature uniformity is characterized by adding auxiliary materials containing temperature-sensitive electromagnetic materials inside, outside or both inside and outside a material, so that the heating capacity of the whole material or a certain local area in a required temperature interval is reduced along with the temperature rise, and the heating capacity of a hot area in the whole material or a certain local area in the temperature interval is lower than that of a cold area, so that the temperatures of the hot area and the cold area are closer, as shown in figure 1.
Adding an auxiliary material containing a temperature-sensitive electromagnetic material into a material (not shown in the figure) means that powder containing the temperature-sensitive electromagnetic material, such as particles of materials including strontium titanate, barium strontium titanate and the like and mixtures thereof, is mixed in the material, so that the material obtains wave-absorbing performance which is reduced along with the temperature rise in a required temperature range. The method for mixing the temperature-sensitive electromagnetic material in the material is determined according to the aspects of the shape, the size and the like of the material, such as melt blending, mechanical blending and the like.
Adding an auxiliary material containing a temperature-sensitive electromagnetic material outside the material means that a temperature-sensitive film with a two-layer or multi-layer structure is covered outside the material, as shown in fig. 2; the temperature-sensitive film is composed of one or more dielectric layers and one or more sub-wavelength conductive patterns, and at least one dielectric layer or conductive pattern is made of or contains a temperature-sensitive electromagnetic material, so that the wave absorbing performance of the whole temperature-sensitive film and material is reduced along with the temperature rise in a required temperature interval. The conductive pattern has a negligible dimension in the thickness direction (less than 500 μm), has a specific geometrical shape in-plane (e.g. square ring shape of fig. 2), and the shape and dimension thereof are easily determined by electromagnetic simulation in the case of material selection (i.e. material parameter determination). The auxiliary material containing the temperature-sensitive electromagnetic material is added outside the material, namely, the wave-absorbing material is covered outside the material; the wave-absorbing material is made of or comprises a temperature-sensitive electromagnetic material, and has wave-absorbing performance which is reduced along with the temperature rise in a required temperature range, so that heat is transferred to a heated material more uniformly after microwave is absorbed. When the auxiliary material containing the temperature-sensitive electromagnetic material is added outside the material, special attention needs to be paid to ensure that the auxiliary material is in close contact with the heated material, and the method can be realized by methods such as coating, attaching, plating, vacuum adsorption and the like. The temperature-sensitive electromagnetic material refers to a material with electromagnetic parameters changing along with temperature; alloys of metals such as copper, aluminum, silver, chromium, etc., phase-change metal oxides such as vanadium dioxide, etc., ferroelectric materials such as strontium titanate, barium titanate, etc., liquid crystal materials, and materials containing the above components. The electromagnetic parameters refer to resistivity, dielectric constant, magnetic permeability or a combination of the above parameters.
The invention will now be further illustrated by the following examples.
Example 1.
The microwave heating outer part is covered with a carbon fiber reinforced epoxy resin matrix composite material with a temperature-sensitive film with a two-layer structure. The carbon fiber reinforced epoxy resin-based composite material is formed by manually laying unidirectional prepreg, and the laying angle is 0 degree/90 degree]10The size of the composite material is 250 (length) multiplied by 250 (width) multiplied by 2 (height) mm3. As shown in FIG. 2, the temperature-sensitive film with double-layer structure comprises a conductive pattern and a dielectric layer, wherein the upper conductive pattern is made of copper with a thickness of 18 μm and a conductivity of 5.813 × 107And S/m, wherein the shape of the S/m is a square annular unit, the S/m is arranged on the dielectric layer in an array mode, and the pattern is obtained by etching the copper foil through laser. The dielectric layer is prepared by uniformly mixing and curing epoxy resin and strontium titanate powder according to the mass ratio of 1:1, the thickness is 0.52mm, and the particle size of the strontium titanate powder is 1 mu m. The real part of the dielectric constant of the dielectric layer material at the frequency of 2.45GHz is monotonically increased along with the temperature rise within the range of 25-150 ℃, and the change situation is shown in figure 3. Temperature-sensitive film with double-layer structure and [0 °/90 ° ]]10The overall absorptivity of the carbon fiber reinforced epoxy resin-based composite material' to 2.45GHz microwaves is reduced from 91.28% at 25 ℃ to 57.17% at 150 ℃, and the change condition is shown in figure 4. The double-layer temperature-sensitive film is adsorbed on the carbon fiber reinforced epoxy resin matrix composite material in a vacuum mode through a vacuum bag and placed in a microwave heating cavity to be heated, and temperature uniformity is greatly improved.
Example 2.
The microwave heating outer part is covered with a glass fiber plate containing a wave-absorbing material of a temperature-sensitive material. Using the "double-layer junction" in example 1Structure temperature sensitive film and [0 °/90 ° ]]10The carbon fiber reinforced epoxy resin matrix composite material is integrally used as a wave-absorbing material containing a temperature-sensitive material and is covered on a wave-absorbing material with the size of 250 (length) multiplied by 250 (width) multiplied by 2 (height) mm3The glass fiber board is provided with a temperature-sensitive film with a double-layer structure and a temperature of 0 degree/90 degree]10The carbon fiber reinforced epoxy resin matrix composite absorbs microwaves integrally to generate heat, and transfers the heat to the glass fiber board more uniformly.
Example 3.
And heating the epoxy resin internally mixed with the temperature-sensitive material by microwave. Uniformly mixing bisphenol A type epoxy resin and a curing agent thereof according to the mass ratio of 10:3, and pouring the mixture into a mold with the size of 200 (length) multiplied by 200 (width) multiplied by 50 (height) mm3In the silica gel mold. Then, barium strontium titanate nano powder (Ba) with the mass ratio of 1:2 to the epoxy resin is doped into the epoxy resin0.6Sr0.4TiO3) The absorptivity of the mixture to 915MHz microwave is monotonously reduced in 25-150 ℃. Placing the microwave heating chamber in a microwave heating chamber, and uniformly heating the microwave heating chamber at a temperature range of 25-120 ℃.
The parts not involved in the present invention are the same as or can be implemented using the prior art.
Claims (5)
1. A method for improving the uniformity of microwave heating temperature is characterized in that: the auxiliary material containing the temperature-sensitive electromagnetic material is added in, outside or both the inside and the outside of the material, so that the heating capacity of the whole material or a certain local area in a required temperature interval is reduced along with the temperature rise, and the heating capacity of a hot area in the whole material or a certain local area in the temperature interval is lower than that of a cold area, so that the temperatures of the hot area and the cold area are enabled to be closer.
2. The method of claim 1, wherein: the addition of the auxiliary material containing the temperature-sensitive electromagnetic material into the material means that powder containing the temperature-sensitive electromagnetic material is mixed into the material, so that the material obtains the wave-absorbing performance which is reduced along with the temperature rise in a required temperature range.
3. The method of claim 1, wherein: adding an auxiliary material containing a temperature-sensitive electromagnetic material outside the material means that a temperature-sensitive film with a two-layer or multi-layer structure is covered outside the material; the temperature-sensitive film is composed of one or more dielectric layers and one or more sub-wavelength conductive patterns, and at least one dielectric layer or conductive pattern is made of or contains a temperature-sensitive electromagnetic material, so that the wave absorbing performance of the whole temperature-sensitive film and material is reduced along with the temperature rise in a required temperature interval.
4. The method of claim 1, wherein: adding an auxiliary material containing a temperature-sensitive electromagnetic material outside the material means that a wave-absorbing material is covered outside the material; the wave-absorbing material is made of or comprises a temperature-sensitive electromagnetic material, and has wave-absorbing performance which is reduced along with the temperature rise in a required temperature range, so that heat is transferred to a heated material more uniformly after microwave is absorbed.
5. The method of claim 1, wherein: the temperature-sensitive electromagnetic material refers to a material with electromagnetic parameters changing along with temperature; the electromagnetic parameters refer to resistivity, dielectric constant, magnetic permeability or a combination of the above parameters.
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Citations (9)
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| US5079397A (en) * | 1987-11-18 | 1992-01-07 | Alcan International Limited | Susceptors for microwave heating and systems and methods of use |
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2021
- 2021-11-25 CN CN202111410642.5A patent/CN114222387A/en active Pending
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| GB1592978A (en) * | 1976-10-08 | 1981-07-15 | Pillsbury Co | Microwave food heating package method of heating such package containing food food so heated and combination of oven and microwave food heating package |
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| CN112455048A (en) * | 2020-11-24 | 2021-03-09 | 南京航空航天大学 | Microwave high-efficiency heating method for strong reflection material |
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